<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>登陆表单及高亮按钮显示</title>
    <style>
        html{
            height: 100%;
        }
        body{
            margin:0;
            padding: 0;
            font-family: sans-serif;
            background: linear-gradient(#123123,#12311e);
        }
        .login-box{
            position:absolute;
            top:50%;
            left:50%;
            width: 400px;
            padding: 2em;
            transform:translate(-50%,-50%);
            background:rgba(0,1,2,0.3);
            box-sizing:border-box;
            box-shadow:0 10px 25px rgba(0,0,0,0.6);
            border-radius: 10px;
        }
        .login-box h2{
            margin:0 0 30px;
            padding:0;
            color:#fff;
            text-align: center;
        }
        .login-box .user-box{
            position: relative;
        }
        .login-box .user-box input{
            width: 100%;
            padding:10px 0;
            font-size: 16px;
            color:#fff;
            margin-bottom: 30px;
            border:none;
            border-bottom: 1px solid #fff;
            outline: none;
            background: transparent;
        }
        .login-box .user-box label{
            position: absolute;
            top:0;
            left: 0;
            padding: 10px 0;
            font-size: 16px;
            color: #fff;
            pointer-events: none;
            transition: 0.5s;
        }
        .login-box .user-box input:focus ~ label,
        .login-box .user-box input:valid ~ label{
            top:-20px;
            left:0;
            color: #fffccc;
            font-size: 12px;
        }
        .login-box form a{
            position: relative;
            display: inline-block;
            padding: 10px 20px;
            color: #fff;
            font-size: 16px;
            text-decoration: none;/*属性规定添加到文本的修饰*/
            text-transform: uppercase;
            overflow: hidden;
            transition: 0.5s;
            margin-top:40px;
            letter-spacing: 5px;
        }
        .login-box a:hover{
            background: #03e9f4;
            color: #fff;
            border-radius: 5px;
            box-shadow: 0 0 5px #03e9f4,
                        0 0 25px #03e9f4,
                        0 0 50px #03e9f4,
                        0 0 100px #03e9f4;
        }
        .login-box span{
            position: absolute;
            display: block;
        }
        .login-box a span:nth-child(1){
            top:0;
            left:-100%;
            width: 100%;
            height: 2px;
            background: linear-gradient(90deg,transparent,#03e9f4);
            animation:btn-anim1 2s linear infinite;
        }
        @keyframes btn-anim1{
            0% {
                left:-100%;
            }
            50%,100%{
                left:100%;
            }
        }
        .login-box a span:nth-child(2){
            top:-100%;
            right:0;
            width: 2px;
            height: 100%;
            background: linear-gradient(180deg,transparent,#03e9f4);
            animation:btn-anim2 2s linear infinite;
            animation-delay: 0.5s;
        }
        @keyframes btn-anim2{
            0% {
                top:-100%;
            }
            50%,100% {
                top:100%;
            }
        }
        .login-box a span:nth-child(3){
            bottom:0;
            right:-100%;
            width: 100%;
            height: 2px;
            background: linear-gradient(270deg,transparent,#03e9f4);
            animation:btn-anim3 2s linear infinite;
            animation-delay: 1s;
        }
        @keyframes btn-anim3{
            0% {
                right:-100%;
            }
            50%,100% {
                right:100%;
            }
        }
        .login-box a span:nth-child(4){
            bottom:-100%;
            left:0;
            width:2px;
            height: 100%;
            background: linear-gradient(360deg,transparent,#03e9f4);
            animation:btn-anim4 2s linear infinite;
            animation-delay: 1.5s;
        }
        @keyframes btn-anim4{
            0% {
                bottom:-100%;
            }
            50%,100% {
                bottom:100%;
            }
        }
    </style>
</head>
<body>
    <p>https://codepen.io/soufiane-khalfaoui-hassani/pen/LYpPWda</p>
    <div class="login-box">
        <h2>logic</h2>
        <form action="">
            <div class="user-box">
                <input type="text" name="" required>
                <label for="">用户名</label>
            </div>
            <div class="user-box">
                <input type="password" name="" required>
                <label for="">密码</label>
            </div>
            <a href="#">
                <span></span>
                <span></span>
                <span></span>
                <span></span>
                提交
            </a>
        </form>
    </div>
</body>

</html>